hi all i have an elegance coral which appears fine but when it retracts at night a small portion of the tissue has been lifted away from the skeleton and inside is a small stony looking crab, he seems to use his shell as a trap door, i re searched this and it appears to be a gall crab, are these real bad? should i remove him?, alot of the info i read did not go into much detail, (i only found a few brief write ups) is this crab eating my elegance? the coral expands well but the disc the crab is living uder, the tentacles dont extend as long as the rest? thanks.